Seed production and seedling establishment of a Southwest riparian tree, Arizona walnut ( Juglans major )

A four-year study of five populations has revealed influences on seed production and seedling establishment of the Southwest riparian tree Juglans major . Germination is abundant after production of large seed crops (masts), but masts are produced infrequently. Within years, germination is stimulated by summer rains, enabling seedlings to establish on riparian terraces as well as streambanks. Traits such as capacity for dormancy during summer drought allow some seedlings to survive on terraces, but abundant rainfall is essential for high rates of seedling success. Ranges of moisture tolerance vary among seeds collected from different populations, suggesting that ecotypes may exist between riparian sites with dissimilar moisture regimes. Population-based differences are associated, in part, with differences in seed size.     

Woody riparian vegetation response to different alluvial water table regimes

Woody riparian vegetation in western North American riparian ecosystems is commonly dependent on alluvial groundwater. Various natural and anthropogenic mechanisms can cause groundwater declines that stress riparian vegetation, but little quantitative information exists on the nature of plant response to different magnitudes, rates, and durations of groundwater decline. We observed groundwater dynamics and the response of Populus fremontii , Salix gooddingii , and Tamarix ramosissima saplings at 3 sites between 1995 and 1997 along the Bill Williams River, Arizona. At a site where the lowest observed groundwater level in 1996 (-1.97 m) was 1.11 m lower than that in 1995 (-0.86 m), 92-100% of Populus and Salix saplings died, whereas 0-13% of Tamarix stems died. A site with greater absolute water table depths in 1996 (-2.55 m), but less change from the 1995 condition (0.55 m), showed less Populus and Salix mortality and increased basal area. Excavations of sapling roots suggest that root distribution is related to groundwater history. Therefore, a decline in water table relative to the condition under which roots developed may strand plant roots where they cannot obtain sufficient moisture. Plant response is likely mediated by other factors such as soil texture and stratigraphy, availability of precipitation-derived soil moisture, physiological and morphological adaptations to water stress, and tree age. An understanding of the relationships between water table declines and plant response may enable land and water managers to avoid activities that are likely to stress desirable riparian vegetation.     

Localization of the binding site for the human high-affinity Fc receptor on IgG

A major pathway in the clearance of pathogens involves the coating of the pathogen with specific antibodies, and the binding of the antibody Fc region to cell receptors. This can trigger engulfment of the pathogen by phagocytes or lysis by killer cells. By oligonucleotide site-directed mutagenesis we have engineered a single amino acid change in a mouse IgG2b antibody (Glu 235----Leu) which now enables the antibody to bind to the FcRI (high affinity) receptor on human monocytes with a 100-fold improvement in affinity. This indicates that Leu 235 is a major determinant in the binding of antibody to FcRI and that the receptor may interact directly with the region linking the CH2 domain to the hinge. Tailoring the affinity of antibodies for cell receptors could help dissect their role in clearing pathogen.     

Dantrolene and the effect of temperature on the spontaneous release of transmitter at the frog neuromuscular junction

The characteristic effect of temperature on m.e.p.p. frequency at the amphibian neuromuscular junction is unaltered by the presence of Dantrolene (an agent that is believed to reduce the efflux of Ca2+ from intracellular stores) or by changes in [Ca2+)o. It is concluded that temperature affects the release system directly, with a transition temperature at about 16 degrees C.     

Differential olfactory perception of enantiomeric compounds by blind subterranean mole rats (Spalax ehrenbergi)

The behavior of mole rats (Spalax ehrenbergi) near pairs of enantiomeric compounds was examined in 901 two-choice experimental tests. Positioning of the nest and food store and the preferred location of the tested animal were used to assess attraction or aversion to the tested odorants. The results indicated that mole rats respond differentially to odors of stereoisomers (enantiomers of carvone, citronellol, and fechone). They responded to one enantiomer of each tested pair but were indifferent to or did not smell the other. Both sexes were attracted to the odor of R-(–)-carvone and repelled by the odor of (+)-citronellol. Females were attracted to the odor of (–)-fenchone while males had no preference. By contrast, all animals were indifferent to or did not smell the odor of S-(+)-carvone, (–)-citronellol, and (+)-fenchone. Further research to distinguish between these alternatives (indifference vs hyposmia/anosmia) is suggested.     

Extensive allelic variation and ultrashort telomeres in senescent human cells

By imposing a limit on the proliferative lifespan of most somatic cells, telomere erosion represents an innate mechanism for tumor suppression and may contribute to age-related disease. A detailed understanding of the pathways that link shortened telomeres to replicative senescence has been severely hindered by the inability of current methods to analyze telomere dynamics in detail. Here we describe single telomere length analysis (STELA), a PCR-based approach that accurately measures the full spectrum of telomere lengths from individual chromosomes. STELA analysis of human XpYp telomeres in fibroblasts identifies several features of telomere biology. We observe bimodal distributions of telomeres in normal fibroblasts; these distributions result from inter-allelic differences of up to 6.5 kb, indicating that unexpectedly large-scale differences in zygotic telomere length are maintained throughout development. Most telomeres shorten in a gradual fashion consistent with simple losses through end replication, and the rates of erosion are independent of allele size. Superimposed on this are occasional, more substantial changes in length, which may be the consequence of additional mutational mechanisms. Notably, some alleles show almost complete loss of TTAGGG repeats at senescence.     

The European dimension for the mouse genome mutagenesis program

The European Mouse Mutagenesis Consortium is the European initiative contributing to the international effort on functional annotation of the mouse genome. Its objectives are to establish and integrate mutagenesis platforms, gene expression resources, phenotyping units, storage and distribution centers and bioinformatics resources. The combined efforts will accelerate our understanding of gene function and of human health and disease.